Conventionally, a high voltage metal-oxide-semiconductor field-effect transistor (HV MOSFET) device has a circular configuration. From the top view of the circular HV MOSFET device, the central portion is the drain region, and the outer portion enclosing the drain region is the source region. In addition, the width of the channel region of the circular HV MOSFET device is determined according to the circumference of the intermediate zone between the drain region and the source region. A conventional approach of increasing the conduction current of the HV MOSFET device is to increase the radius of the HV MOSFET device. However, the increase of the radius of the HV MOSFET device will increase the area of the HV MOSFET device.
For increasing the conduction current of the HV MOSFET device while minimizing the area of the HV MOSFET device, a race-track HV MOSFET device and an M-type HV MOSFET device have been disclosed. By contrast, the use of the M-type HV MOSFET device can achieve a higher conduction current.
By the conventional manufacturing processes, the breakdown voltage (BDV) of the M-type HV MOSFET device is lower than each of the breakdown voltage of the circular HV MOSFET device and the breakdown voltage of the race-track HV MOSFET device. For simultaneously forming the three types of HV MOSFET devices on the same integrated circuit, the voltage-withstanding capability of the overall integrated circuit is deteriorated because of the limitation of the breakdown voltage of the M-type HV MOSFET device.
The present inventors found that the conventional M-type HV MOSFET device has so many round corners. Due to the round corners, the M-type HV MOSFET device has higher electric field and higher electric current in some specified sites. Under this circumstance, the voltage-withstanding capability of these specified sites will be impaired, and thus the breakdown voltage of the overall M-type HV MOSFET device is deteriorated. For solving the above drawbacks, a high voltage MOS transistor and fabricating method thereof are disclosed in a co-pending U.S. patent application Ser. No. 13/216,276, which was filed by the same assignee of the present application. However, the performance is still unsatisfied.
Therefore, there is a need of providing an improved HV MOSFET device for increasing the breakdown voltage in order to integrate various shapes of HV MOSFET devices.